The invention concerns a method for generating magnetic resonance (MR) images or MR spectra of at least one partial area of a moving object with at least one motion sequence that is repeated during consecutive motion states.
A method of this type has been disclosed in DE 10 2006 002 982 B4 (US patent application 2007/0238972 A1).
Magnetic resonance (MR) methods, in particular nuclear magnetic resonance (NMR) methods, are used for a wide variety of purposes for obtaining image information or also chemical information about objects. In clinical applications, living objects, e.g. human beings or animals or individual body parts of human beings and animals are thereby regularly examined.
When an object moves during the MR measurement, the quality of the measurement may be impaired. With respect to image recordings, the image may e.g. be blurred. In general, one tries to keep the object stationary during the measurement. Human patients may e.g. be asked not to move and animals may be anaesthetized.
Some motion processes, usually repetitive motion processes, are part of the basic functions of life and cannot be avoided, such as e.g. the heart beat or respiration.
In order to reduce the influence of repetitive motions on an MR measurement, the motions of the object are normally monitored and the MR measurements are performed within a time slot, in which the motion is interrupted or is at a minimum, e.g. between two heart beats. The MR measurements are then triggered via a suitable monitor signal.
However, it is sometimes desired to precisely observe changes in an object during a repetitive motion sequence. The changes in the object during such a repetitive motion sequence are generally relatively small such that the deteriorated quality of the MR measurement caused by the motion renders observation of these changes impossible.
DE 10 2006 002 982 B4 (US patent application 2007/0238972 A1) discloses determination of one function f(t) of the time shift for each individual MR image and phase-correcting the measured data of the individual MR images in correspondence with their motion state. It is thereby possible to keep the position of a moving partial area in a spatially stationary state after data processing.
This procedure can improve the data quality only in a limited number of situations. When e.g. slice selection is used within the scope of the MR measurement, compensation can be effected through back calculation only in the plane. When the motion of the object disturbs measurement variables other than direct motion of the object per se, e.g. a time variation of the local strength of a gradient field, the disturbance in the individual MR images cannot be back calculated and the quality of the measured MR data cannot be improved.
It is therefore the underlying purpose of the present invention to provide a method for improving the quality of MR measurements of moving objects, in particular, when back calculation of disturbances in the measured MR measured data is not possible.